Heat exchanger systems and methods

ABSTRACT

Disclosed herein are heat exchanger system comprising: a refrigerant; a phase-changing material in thermal communication with the refrigerant; and a valve configured to selectively permit an amount of the refrigerant to flow through the heat exchanger system, the amount of the refrigerant being based on a temperature difference between the refrigerant and the phase-changing material. Also disclosed herein are methods of using the same.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to heat exchanger systems and methods and, in particular, to heat exchanger systems and methods that include phase-changing materials.

BACKGROUND

The technological field of cooling materials has proven vital to human survivability. For instance, air-conditioning has allowed humans to live in environments previously thought to be uninhabitable, and refrigeration has increased the world's access to food. As the human population continues to grow, there is an increased demand not only for improved cooling methods, but improved cooling methods utilizing energy- and cost-effective methods. During cooler times (e.g., during the night), the energy load on such air-cooling systems can be typically reduced, which can result is comparatively high energy efficiency as compared to hotter times (e.g., during the day) when the energy load on air-cooling systems can typically be increased, thus requiring more energy and driving up costs. Unfortunately, while cooling during cooler times is more energy efficient, there is typically less demand for cooling during cooler times.

What is needed, therefore, are methods and systems to further increase the overall efficiency of the system. The present disclosure addresses this need as well as other needs that will become apparent upon reading the description below in conjunction with the drawings.

BRIEF SUMMARY

The present disclosure relates generally to heat exchanger systems and methods. Particularly, the present disclosure relates to heat exchanger systems and methods utilizing phase-changing materials. The disclosed technology includes a heat exchanger system for use with a cooling system, and the heat exchanger system can comprise a phase-changing material in thermal communication with a refrigerant flow path, and a valve configured to selectively permit an amount of the refrigerant to flow through the heat exchanger system. The refrigerant flow path can be configured to allow refrigerant to flow through the heat exchanger system. The amount of refrigerant allowed to flow through the system can be based on a temperature difference between the refrigerant and the phase-changing material. Depending on the application, the heat exchanger system can be installed upstream of a condenser in a vapor compression cycle, upstream of an evaporator in a vapor compression cycle, or in any other useful position within a vapor compression cycle.

The heat exchanger system can comprise a controller in communication with the valve and one or more sensors. The controller can be configured to receive temperature data from the one or more sensors and control the valve based on the temperature data.

The refrigerant can be configured to flow through the heat exchanger system at a median refrigerant temperature. The phase-changing material can have a melting point such that the difference between the melting point and the median refrigerant temperature is in the range from approximately 0° F. to approximately 10° F. For example, the phase-changing material can be a paraffin wax.

The valve can have a degree of openness corresponding to the temperature difference between the refrigerant and the phase-changing material. Additionally, the valve can have an open state and a closed state wherein the degree of openness is completely open in the open state and completely closed in the closed state.

The valve can further be configured to enter the closed state when the median refrigerant temperature and the temperature of the phase-changing material are substantially equivalent. In other words, the valve can close when the materials are in thermal equilibrium.

The valve can further be configured to transition to the open state when the temperature difference is greater than a predetermined threshold. During the transition to the open state, the degree of openness can be proportional to the magnitude of the temperature difference.

The capacity of the heat exchanger system can be defined in terms of the thermal storage capacity expressed in British Thermal Units (BTUs) or kilowatt-hours. If such a heat exchanger system is meant for partial cooling during peak load periods, for instance, the total thermal storage capacity of the system can be the sum of the partial cooling load in BTU/Hr or kW for the duration of the peak load conditions.

The disclosed technology includes a cooling system, and the cooling system can comprise a refrigerant, a refrigerant flow path, one or more components in communication with the refrigerant flow path, and a heat exchanger system. The one or more components can include one or more of: a compressor, a condenser, an evaporator, and a thermal expansion valve. The heat exchanger system can comprise a phase-changing material in thermal communication with the refrigerant flow path, and a valve configured to selectively permit an amount of the refrigerant to flow through the heat exchanger system. The amount of refrigerant allowed to flow through the system can be based on a temperature difference between the refrigerant and the phase-changing material.

The heat exchanger system can comprise a controller in communication with the valve and one or more sensors. The controller can be configured to receive temperature data from the one or more sensors and control the valve based on the temperature data.

The refrigerant can be configured to flow through the heat exchanger system at a median refrigerant temperature. The phase-changing material can have a melting point such that the difference between the melting point and the median refrigerant temperature is in the range from approximately 0 to approximately 10° F.

The valve can be configured to transition between a plurality of states. For example, the plurality of states can include an open state and closed state. The plurality of states can further include one or more intermediate states corresponding to the temperature difference between the phase-changing material and the median refrigerant temperature.

The valve can further be configured to enter the closed state when the median refrigerant temperature of the refrigerant and the temperature of the phase-changing material are substantially equivalent. In other words, the valve can close when the materials are in thermal equilibrium. The valve can further be configured to transition to the open state when the temperature difference is greater than a predetermined threshold.

The disclosed technology includes a method of capturing cooling energy during partial-load cycles in a cooling system. The method can include providing a heat exchanger comprising a phase-changing material in thermal communication with a refrigerant and providing a valve configured to selectively permit the refrigerant to flow through the heat exchanger. The method can include, in response to the median refrigerant temperature being less than the melting point, transitioning the valve to an open state such that the refrigerant can flow through the heat exchanger, thereby effecting heat transfer between the refrigerant and the phase-change material to cause the phase-changing material to become at least partially solidified. The method can include transitioning the valve to a closed state in response to the phase-changing material reaching thermal equilibrium with the refrigerant.

The method can include, responsive to the refrigerant temperature being greater than the melting point of the phase-changing material, transitioning the valve to the open state such that the refrigerant can flow through the heat exchanger, thereby effecting heat transfer between the refrigerant and the phase-change material to cause the phase-changing material to become at least partially melted.

Also disclosed herein are methods of reusing stored cooling energy to improve the overall efficiency of high-load cycles in an air-cooling system.

These and other aspects of the present disclosure are described in the Detailed Description below and the accompanying figures. Other aspects and features of examples of the present disclosure will become apparent to those of ordinary skill in the art upon reviewing the following description of specific examples of the present disclosure in concert with the figures. While features of the present disclosure may be discussed relative to certain examples and figures, all examples of the present disclosure can include one or more of the features discussed herein. Further, while one or more examples may be discussed as having certain advantageous features, one or more of such features may also be used with the various examples of the disclosure discussed herein. In similar fashion, while examples may be discussed below as device, system, or method examples, it is to be understood that such examples can be implemented in various devices, systems, and methods of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate multiple examples of the presently disclosed subject matter and serve to explain the principles of the presently disclosed subject matter. The drawings are not intended to limit the scope of the presently disclosed subject matter in any manner.

FIG. 1 illustrates an example cooling system utilizing a heat exchanger system, in accordance with the present disclosure.

FIG. 2 illustrates an example heat exchanger system, in accordance with the present disclosure.

FIG. 3 illustrates an example controller for a heat exchanger system and/or a cooling system, in accordance with the present disclosure.

FIG. 4A illustrates a pressure-enthalpy chart of an example cooling system under low-load without a heat exchanger system, in accordance with the present disclosure.

FIG. 4B illustrates a pressure-enthalpy chart of an example cooling system under low-load with a heat exchanger system, in accordance with the present disclosure.

FIG. 5A illustrates a pressure-enthalpy chart of an example cooling system under high-load without a heat exchanger system, in accordance with the present disclosure.

FIG. 5B illustrates a pressure-enthalpy chart of an example cooling system under high-load with a heat exchanger system, in accordance with the present disclosure.

FIG. 6 illustrates a flowchart of an example cycle for capturing cooling energy during partial-load times and reusing the captured cooling energy during high-load times, in accordance with the present disclosure.

FIG. 7 illustrates a flowchart of an example method of controlling a heat exchanger system, in accordance with the present disclosure.

FIG. 8 illustrates a flowchart of an example method of controlling a heat exchanger system, in accordance with the present disclosure.

DETAILED DESCRIPTION

Heat exchangers utilize temperature differences between materials to drive a transfer of heat from one material to the other. The heat transfer rate and efficiency of a heat exchanger typically increases as the temperature difference between the materials increases. If a system could store energy when there is a comparatively low demand for cooling and use the stored energy when the demand for cooling is comparatively high, the overall efficiency of the system could increase, and the overall energy consumption of the system could decrease.

In a typical air-cooling system, an evaporator section can be exposed to indoor conditioned air, and a condenser section can be exposed to outdoor unconditioned air. A thermal expansion valve (TXV) can control the system based on the temperature difference of the indoor air and outside air. In response to the temperature difference becoming greater than a threshold value, the TXV can be configured to transition to an open position, which can permit an increased amount of refrigerant to flow therethrough. This in turn increases the pressure and temperature of the refrigerant entering the evaporator section, decreasing the overall energy efficiency of the HVAC system. Alternatively, in response to the temperature difference becoming less than a threshold value, the TXV can be configured to transition to a closed position, allowing less refrigerant to flow through the system. This process in turn decreases the pressure and temperature of the refrigerant entering the evaporator section, increasing the overall energy efficiency of the system. In other words, such methods and systems can improve energy efficiency and reduce costs of air-cooling systems by taking advantage of comparatively high energy efficiency of cooling during low-load periods in order to reduce energy usage during high-load periods.

The disclosed technology includes the use of other dynamic valve devices and systems, such as capillary tubes, electronic expansion valve (EXV), and the like. While various examples are discussed herein with respect to a TXV, it is within the scope of the disclosure that the example systems can include alternate dynamic valve systems alternatively or in addition the TXV expressly discussed.

The present disclosure provides systems and methods for storing and reusing cooling energy to reduce overall energy consumption of cooling systems, such as refrigeration systems; heating, ventilation, and air-conditioning (HVAC) systems; air-conditioning systems; central air systems; automobile coolant systems; and the like. The systems and methods disclosed herein include heat exchangers containing a phase-changing material. The phase-changing material can have a high latent heat of melting, requiring a large amount of added energy to transition the phase-changing material between the solid and liquid phases. During cooler, low-load times, the system can transfer heat away from the phase-changing material to solidify the phase-changing material. The cooling energy, therefore, can be stored in the solidified phase-changing material. Subsequently, during hotter, high-load times, the cold and solidified phase-changing material can transfer heat away from the system until the phase-changing material reverts back to a liquid (e.g., melts). In other words, cooling energy can be stored in the solidified phase-changing material and subsequently used to reduce energy loads and improve the efficiency of the system.

Although certain examples of the disclosure are explained in detail, it is to be understood that other examples and applications are contemplated. Accordingly, it is not intended that the disclosure is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. Other examples of the disclosure are capable of being practiced or carried out in various ways. Also, in describing the disclosed technology, specific terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Herein, the use of terms such as “having,” “has,” “including,” or “includes” are open-ended and are intended to have the same meaning as terms such as “comprising” or “comprises” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” are intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified.

The components described hereinafter as making up various elements of the disclosure are intended to be illustrative and not restrictive. Many suitable components that would perform the same or similar functions as the components described herein are intended to be embraced within the scope of the disclosure. Such other components not described herein can include, but are not limited to, for example, similar components that are developed after development of the presently disclosed subject matter.

Reference will now be made in detail to examples of the disclosed technology, some of which are illustrated in the accompanying drawings. Wherever convenient, the same references numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 1 illustrates a cooling system 100 comprising a heat exchanger system 200. The cooling system can further comprise an evaporator 110, a compressor 120, a condenser 130, and a thermal expansion valve 140. Additionally, the refrigerant can flow through refrigerant flow path 210 as in FIG. 2. The heat exchanger system 200 can be positioned in a variety of positions within the cooling system 100 to maximize energy efficiency. As shown, the heat exchanger system 200 can be positioned as a bypass parallel to the refrigerant flow path 210 and the rest of the cooling system 100. Such a parallel bypass configuration can optimize the timing of the heat transfer as the valve 230 can limit the amount of refrigerant interacting with the phase-changing material 220. It is understood, however, that the heat exchanger system 200 can be placed in other configurations with the cooling system 100, such as in series with the other components, as desired to optimize the heat transfer and energy storage in the phase-changing material 220. The phase-changing material 220 can additionally be selected or altered based on the position of the heat exchanger system. For example, a phase-changing material 220 with a higher melting point can be selected if the heat exchanger system 200 is on the hotter liquid line, as opposed to a lower melting point if the heat exchanger system 200 is on the colder suction line.

As shown in FIG. 2, a heat exchanger system 200 can comprise a refrigerant (illustrated by a refrigerant flow path 210), a phase-changing material 220, and a valve 230. The valve 230 can be configured to selectively permit flow of the refrigerant through the refrigerant flow path 210, and the refrigerant can have a predetermined median refrigerant temperature. The phase-changing material 220 can have a predetermined melting point. The valve 230 can be configured to remain closed until the difference between the median refrigerant temperature and the current temperature of the phase-changing material 220 exceeds a predetermined threshold. In response to the difference between the median refrigerant temperature and the current temperature of the phase-changing material 220 exceeding the predetermined threshold, the valve 230 can be configured to begin opening and/or transitioning to the open state (e.g., continuously or stepwise) to selectively permit the refrigerant to flow through refrigerant flow path 210. Therefore, the refrigerant can be permitted to thermally communicate with the phase-changing material 220 via the refrigerant flow path 210. The valve 230 can continue to permit thermal communication between the refrigerant and the phase-changing material 220 until the refrigerant and the phase-changing material 220 reach thermal equilibrium. Once the temperatures of the refrigerant and the phase-changing materials 220 are approximately equal, the valve 230 can be configured to close and/or transition to the closed state (e.g., continuously or stepwise). Accordingly, the cooling effect of the refrigerant can be stored in the phase-changing material.

The amount of the refrigerant permitted to flow into thermal communication with the phase-changing material 220 can be based on a temperature difference between the refrigerant and the phase-changing material 220. The refrigerant can be configured to flow through the heat exchanger system 200 at a median refrigerant temperature. The type of phase-changing material 220 used for a given system can be selected based on having a melting point closer to the operating temperature of the refrigerant. For example, the phase-changing material 220 can be selected such that there is a temperature difference between the melting point and the median refrigerant temperature that is in the range from approximately 0° F. to approximately 10° F. As another example, the phase-changing material 220 can be selected such that there is a temperature difference between the melting point and the median refrigerant temperature that is in the range from approximately 0° F. to approximately 5° F.

The refrigerant can be selected from a variety of materials. The refrigerant can be any material capable of supplying favorable thermodynamic properties to a cooling system. The refrigerant, for example, can be selected based on a desired boiling point, a high heat of vaporization, a moderate liquid density, a high critical temperature, and/or other aspects. Accordingly, the refrigerant can be any chlorofluorocarbon, chlorofluoroolefin, hydrochlorofluorocarbon, hydrochlorofluoroolefin, hydrofluorocarbon, hydrofluoroolefin, hydrochlorocarbon, hydrochloroolefin, hydrocarbon, hydroolefin, perfluorocarbon, perfluoroolefin, perchlorocarbon, perchloroolefin, halon, or haloalkane. For example, the refrigerant can be any refrigerant designated as such by, and compliant with, the standards, rules, and regulations set forth by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) (e.g., ASHRAE Standard 34-2019). For example, the refrigerant can be R-410A or R-134a. It is to be understood, however, that other materials can be used as a refrigerant to transfer heat away from the cooling system 100.

When in use, the refrigerant can flow through the cooling system 100 at a suction temperature. The suction temperature of a refrigerant can refer to the temperature at which the refrigerant cycles when under the suction pressure of the suction line in the cooling system 100. For example, at a suction pressure in the suction line of 100 psig, R-502 can have a suction temperature of 51° F. Because most real-world cooling systems are not perfectly insulated, the suction temperature and pressure may not be constant throughout the suction line or cooling system. Therefore, the median refrigerant temperature of the refrigerant can be used to approximate the overall suction temperature of the refrigerant.

The phase-changing material 220 can be selected based on the refrigerant. For instance, the phase-changing material 220 can be selected to have a melting point near the median refrigerant temperature at which the refrigerant flows through the cooling system 100. The type of phase-changing material used for a given system can be selected based on its melting point. For example, the phase-changing material 220 can be selected such that there is a temperature difference between the melting point and the median refrigerant temperature, at different cooling loads, in the range from approximately 0° F. to approximately 10° F. As another example, the phase-changing material 220 can be selected such that there is a temperature difference between the melting point and the median refrigerant temperature in the range from approximately 0° F. to approximately 5° F. For example, the phase-changing material 220 can be sodium sulfate as sodium sulfate has a melting point of approximately 32° C. and is a known phase-changing material. Alternatively, the phase-changing material 220 can be selected to have a melting point near the average temperature of the environment. For instance, phase-changing materials with higher melting points can be used in hotter climates, while phase-changing materials with lower melting points can be used in colder climates. Because many examples of phase-changing materials can be used and are known, the phase-changing material 220 can be selected based on environmental concerns and/or other factors. Suitable examples of phase-changing materials can include, but are not limited to, molten salts, hydrated salts, and paraffin waxes.

To better retain energy from undergoing a phase change, the phase-changing material 220 can be selected based on its latent heat to transition between the solid and liquid phases. For example, the phase-changing material 220 can have a latent heat of fusion from 200 kJ/kg to 400 kJ/kg (e.g., from 210 kJ/kg to 390 kJ/kg, from 220 kJ/kg to 380 kJ/kg, from 230 kJ/kg to 370 kJ/kg, from 240 kJ/kg to 360 kJ/kg, or from 250 kJ/kg to 350 kJ/kg).

The phase-changing material 220 can be selected such that the absolute difference between the melting point of the phase-changing material 220 and the median refrigerant temperature of the refrigerant is approximately 10° F. or less (e.g., approximately 9.5° F. or less, approximately 9° F. or less, approximately 8.5° F. or less, approximately 8° F. or less, approximately 7.5° F. or less, approximately 7° F. or less, approximately 6.5° F. or less, approximately 6° F. or less, approximately 5.5° F. or less, approximately 5° F. or less, approximately 4.5° F. or less, approximately 4° F. or less, approximately 3.5° F. or less, approximately 3° F. or less, approximately 2.5° F. or less, approximately 2° F. or less, approximately 1.5° F. or less, approximately 1° F. or less, or approximately 0.5° F. or less).

The phase-changing material 220 can alternatively be selected such that the absolute difference between the melting point of the phase-changing material 220 and the median refrigerant temperature of the refrigerant is approximately 0.5° F. or more (e.g., approximately 10° F. or more, approximately 9.5° F. or more, approximately 9° F. or more, approximately 8.5° F. or more, approximately 8° F. or more, approximately 7.5° F. or more, approximately 7° F. or more, approximately 6.5° F. or more, approximately 6° F. or more, approximately 5.5° F. or more, approximately 5° F. or more, approximately 4.5° F. or more, approximately 4° F. or more, approximately 3.5° F. or more, approximately 3° F. or more, approximately 2.5° F. or more, approximately 2° F. or more, approximately 1.5° F. or more, or approximately 1° F. or more,).

The phase-changing material 220 can be selected such that the absolute difference between the melting point of the phase-changing material 220 and the median refrigerant temperature of the refrigerant is in the range from approximately 0.5° F. to approximately 10° F. (e.g., from approximately 0.5° F. to approximately 9.5° F. , from approximately 1° F. to approximately 9° F. , from approximately 1.5° F. to approximately 8.5° F., from approximately 2° F. to approximately 8° F., from approximately 2.5° F. to approximately 7.5° F., from approximately 3° F. to approximately 7° F., from approximately 3.5° F. to approximately 6.5° F., from approximately 4° F. to approximately 6° F., from approximately 4.5° F. to approximately 5.5° F., from approximately 4° F. to approximately 5° F., from approximately 3.5° F. to approximately 5° F., from approximately 3° F. to approximately 5° F., from approximately 2.5° F. to approximately 5° F., from approximately 2° F. to approximately 5° F., from approximately 1.5° F. to approximately 5° F., or from approximately 1° F. to approximately 5° F.).

In the heat exchanger system 200, the phase-changing material 220 can be fluidly separated from the refrigerant. In other words, the phase-changing material 220 and the refrigerant are separate such that no intermixing between the phase-changing material 220 and refrigerant is permitted. This can enable either component to retain its intrinsic properties. While the materials remain fluidly separated, the phase-changing material 220 and the refrigerant can be in thermal communication. This enables the transfer of heat between the phase-changing material 220 and the refrigerant. It is to be understood that materials being fluidly separated does not necessarily require a physical barrier between the fluids; rather, the refrigerant and the phase-changing material 220 can be immiscible liquids, for example. The use of a physical wall or barrier, however, remains a viable option for fluidly separating the refrigerant from the phase-changing material (such as refrigerant flow path 210).

The heat exchangers of the present disclosure can be configured in a variety of designs to accommodate the refrigerant and the phase-changing material 220. Suitable designs of heat exchangers can include, but are not limited to: shell and tube, plate, plate and shell, adiabatic wheel, plate and fin, pillow plate, fluid, waste heat recovery units, dynamic scraped surface, phase-change, microchannel, helical coil, spiral, and the like. While it is described above that the refrigerant and the phase-changing material can be fluidly separated, it is understood that direct contact heat exchangers can be used. For instance, an immiscible liquid-liquid direct contact heat exchanger can be used, or a solid-liquid heat exchanger can be employed.

The heat exchanger system 200 can comprise a valve 230 configured to selectively permit an amount of the refrigerant from the cooling system to flow through the heat exchanger. The valve 230 can be any valve configured to selectively permit refrigerant to pass, which can include, but is not limited to, ball valves, butterfly valves, choke valves, diaphragm valves, gate valves, globe valves, knife valves, needle valves, pinch valves, piston valves, plug valves, solenoid valves, spool valves, and the like. Other valves or other mechanical configurations to selectively permit refrigerant to flow can be used, such as rupture discs or regulators. In addition to valve 230, a second check valve can be included at the outlet of the heat exchanger system 200 on the refrigerant flow path 210. Such an additional check valve can prevent refrigerant from back-flowing into the heat exchanger system, and further preserve the energy stored by the phase-changing material 220.

The valve 230 can be controlled by a mechanical or electronic controller 300. The controller 300 can receive various data (e.g., temperature data, flow data) and provide instructions to various components (e.g., the valve 230) to perform various functionalities described herein (e.g., control of the valve 230). The controller 300 can gather or receive the various data using a one or more sensors 350 (e.g., temperature sensors) and/or one or more transducers 360 (e.g., pressure transducers). Control of the valve 230 can be conducted by a dedicated controller for the heat exchanger system 200 or an overall controller for the cooling system 100. If a dedicated controller is used, the heat exchanger system 200 controller can communicate with a cooling system controller and/or directly with various components of cooling system.

As shown in FIG. 3, the controller 300 can comprise a variety of components for receiving and processing data, as well as components to output instructions. For instance, the controller 300 can comprise one or more processors 310 and memory 320, which can include a program 322 and/or one or more storage devices 324. It should be understood that the controller 300 can receive data from various sensors, process the data, and output one or more instructions to perform one, some, or all of the various functionalities described herein.

The controller can also comprise an analog system. For instance, the controller can be connected to a temperature sensing bulb, such as the temperature sensing bulb in a thermal expansion valve. Other analog temperature and pressure sensors can be used in conjunction with analog systems to implement changes to the valve 230 or to other components of the cooling system 100. For example, the controller can comprise one or more hydraulic lines, pistons, actuators, solenoids, and the like.

The amount of refrigerant permitted to flow through the heat exchanger system 200 can be based on the temperature difference between the refrigerant and the phase-changing material 220 and can be controlled by the valve 230. The valve 230 can have a fully closed state that prevents all flow of refrigerant to the heat exchanger, a fully open state that permits a maximum amount of refrigerant to flow to the heat exchanger system 200, and various intermediate states that permit corresponding intermediate amounts (i.e., less than the maximum amount) of refrigerant to flow to the heat exchanger system 200. As used herein, the phrase “degree of openness” is used to refer to how open or closed the valve 230 is at a given point in time. The degree of openness can correspond to the absolute temperature difference between the refrigerant and the phase-changing material 220. For instance, the degree of openness can be directly proportional to the magnitude of the temperature difference between the refrigerant and the phase-changing material. For example, the valve 230 can be any internally equalized or externally equalized thermal expansion valve.

As mentioned above, the valve 230 can have different degrees of openness other than completely open and completely closed (i.e., the valve 230 can be configured to transition to a “most-open” state that is not the natural fully open state of the valve 230, the valve 230 can be configured to transition to a “most-closed” state that is not the natural fully closed state of the valve 230). The one or more intermediate states can be increased to correspond to the degree of openness and create a smoother transition between the intermediate states. A given degree of openness, therefore, can be a point on a continuous spectrum of states or configurations that are increasingly open or closed, and the degree of openness can be determined based on the temperature difference between the refrigerant and the phase-changing material. Such a gradually transitioning configuration can provide for more precise metering of refrigerant into the heat exchanger based on the detected temperature difference. The continuous or gradual configuration, for example, can be a linear gradient between the open state and the closed state corresponding to the temperature difference between the refrigerant and the phase-changing material.

Rather than having an open state, a closed state and a degree of openness, the valve 230 can be configured to transition between a plurality of discrete states. For example, the plurality of states can include an open state and closed state. The plurality of states can further include one or more intermediate states corresponding to the temperature difference between the phase-changing material and the median refrigerant temperature entering the heat exchanger system. The plurality of states, therefore, can provide a stepwise configuration of intermediate states between the open state and the closed state. For example, the plurality of states can include an open state, closed state, 25% open, 50% open, and 75% open. It is to be understood that other stepwise configurations are contemplated, and that the valve 230 can include more or fewer discrete states.

The valve 230 can further be configured to transition to the fully closed state when the median refrigerant temperature of the refrigerant entering the heat exchanger system and the temperature of the phase-changing material 220 are substantially equivalent. In other words, the valve 230 can fully close when the materials are in thermal equilibrium. The valve 230 can further be configured to transition to an open state (e.g., the fully open state or an intermediate state) when the temperature difference is greater than a predetermined threshold. Alternatively, the valve 230 can gradually transition to the open state from the closed state through the one or more intermediate states based on the temperature difference between the materials. For example, the degree of openness of the valve 230 can directly correspond to the temperature difference between the refrigerant and the phase-changing material. In such a manner, when the refrigerant and phase-changing material 220 reach thermal equilibrium, the valve 230 can close to store energy in the phase-changing material.

FIGS. 4A and 5A illustrate pressure-enthalpy diagrams corresponding to a typical cooling system 100 without a heat exchanger system 200. FIGS. 4B and 5B illustrate, via pressure-enthalpy diagrams, the addition of a heat exchanger system 200 into such a cooling system 100. By way of example only, FIGS. 4A, 4B, 5A, and 5B correspond to the use of R-410A as the refrigerant, but one of skill in the art will recognize that other refrigerants can be used, such as those discussed herein. As shown in FIG. 4B, the addition of a heat exchanger system 200 can consume an amount of enthalpy in the saturated liquid side of a typical vapor compression cycle during low-load operation. This amount of enthalpy consumed can be essentially stored in the solidified phase-changing material 220. As would be appreciated, the large enthalpy change of the saturated liquid refrigerant is not needed during low-load operation, so a portion of the enthalpy changed can be used on the phase-changing material 220 and essentially stored for later use.

During high-load operation, as shown in FIG. 5B, the stored enthalpy is then used to extend the enthalpy change of the saturated liquid during the evaporation step of a typical vapor compression cycle. As would be appreciated, the coefficient of performance for a refrigeration cycle is calculated as the heat absorbed at the lower temperature side divided by the net work of the cycle. Due to the stored enthalpy extending the enthalpy change of the evaporation step, the coefficient of performance in FIG. 5B is greater than that shown in FIG. 5A.

FIG. 6 illustrates a flow chart of a cycle for capturing cooling energy during partial-load times and reusing the captured cooling energy during high-load times. In block 610, the cooling system experiences part-load conditions. For example, a home's HVAC system can have a reduced load during the night time when the external environment is cool. At this point, the cooling system will periodically cycle refrigerant through the system when demanded. Because the cooling system is experiencing part-load conditions, the flow rate of the refrigerant can be reduced such that the saturation temperature of the refrigerant also drops (e.g., the TXV can reduce the cycling refrigerant flow). As the saturation temperature of the cycling refrigerant decreases, the median refrigerant temperature can become lower than the melting point of the phase-changing material, as shown in block 620. The valve can open to allow the refrigerant to enter the heat exchanger system and begin cooling the phase-changing material. The heat energy transferred away from the phase-changing material can induce a phase change from liquid to solid, thereby freezing the phase-changing material. As shown in block 630, this freezing can continue until the solidified phase-changing material and the refrigerant entering the heat exchanger system reach thermal equilibrium. At this point, the valve can close, and the refrigerant can continue cycling through the cooling system, but not the heat exchanger system. In such a manner, the solidified phase-changing material can essentially store cooling energy while remaining sealed off from the rest of the cooling system.

In block 640, the cooling system can experience high-load conditions. For example, a home's HVAC system can require cooling once the sun rises and the hottest part of the day commences. This can represent an increased energy load on the cooling system to meet user demand. Because the cooling system is experiencing high-load conditions, the flow rate of the temperature can be increased such that the saturation temperature of the refrigerant also increase. As the saturation temperature and the external environmental temperature increase, the cycling refrigerant can be cycling through the cooling system at an increased median temperature now higher than the melting point of the phase-changing material, as shown in block 650. As a result, the valve can open once more to allow the refrigerant to enter the heat exchanger system and begin heating the phase-changing material. The heat energy transferred to the phase-changing material can induce a phase change from solid back to liquid, thereby melting the phase-changing material. As shown in block 660, this melting can continue until the melted phase-changing material and the refrigerant entering the heat exchanger system reach thermal equilibrium. At this point, the valve can close, and the refrigerant can continue cycling through the cooling system, but not the heat exchanger system. In such a manner, the phase-changing material can act as a heat sink to transfer heat away from the refrigerant to aid in reducing the energy load needed to cool the refrigerant during high-load operation. Operation can continue until the high-load operation ceases, at which point the cycle can return to block 610 when the cooling system is no longer experiencing peak cooling load.

Both of the following methods disclosed in FIG. 7 and FIG. 8, can comprise the steps of: providing a heat exchanger 200 comprising a phase-changing material 220 in thermal communication with a refrigerant 210, as described above, and providing a valve 230 configured to selectively permit the refrigerant 210 to flow through the heat exchanger 200, wherein the valve 230 has a degree of openness corresponding to a temperature difference between the refrigerant 210 and the phase-changing material 220, as described above.

FIG. 7 illustrates a flowchart of a method 700 of capturing cooling energy during partial-load cycles in a cooling system 100. In block 710, the cooling system 100 can experience part-load conditions such that the median refrigerant temperature at which the refrigerant 210 is entering the heat exchanger system is less than the melting point of the phase-changing material 220. The cooling source can be, for example, the sun setting and the cooler night air acting on the cooling system 100. In block 720, responsive to the median refrigerant temperature of the refrigerant 210 entering the heat exchanger system being less than the melting point of the phase-changing material 220, the valve 230 can be transitioned to an open state to allow refrigerant 210 to come into thermal communication with the phase-changing material 220. The valve 230 can be in the open state such that the phase-changing material 220 is solidified to reach thermal equilibrium with the refrigerant 210. In block 730, responsive to the phase-changing material 220 reaching thermal equilibrium with the refrigerant 210, the valve 230 can be transitioned to a closed state. The method 700 can terminate and complete after block 730. However, alternatively, the method 700 can continue on to other method steps not shown. For instance, the method 700 can proceed to block 810 of the method 800.

FIG. 8 illustrates a flowchart of a method 800 of reusing captured cooling energy to improve the efficiency of high-load cycles in a cooling system 100. It can be appreciated that the method 800 can be used independently, or in conjunction with the method 700. In block 810, the cooling system 100 can experience high-load conditions such that the median refrigerant temperature at which the refrigerant 210 is entering the heat exchanger system is greater than the melting point of the phase-changing material 220. The heat source can be, for example, a user requesting air conditioning to cool their hot house. In block 820, responsive to the median refrigerant temperature of the refrigerant 210 entering the heat exchanger system being greater than the melting point of the phase-changing material 220, the valve 230 can be transitioned to the open state to allow refrigerant 210 to come into thermal communication with the phase-changing material 220. In block 830, responsive to the phase-changing material 220 reaching thermal equilibrium with the refrigerant 210, the valve 230 can be transitioned to the closed state. The method 800 can terminate and complete after block 830. However, alternatively, the method 800 can continue on to other method steps not shown. For instance, the method 800 can proceed to block 710 of the method 700.

Certain examples and implementations of the disclosed technology are described above with reference to block and flow diagrams of systems and methods according to example examples or implementations of the disclosed technology. It will be understood that one or more blocks of the block diagrams and flow diagrams, and combinations of blocks in the block diagrams and flow diagrams, respectively, can be implemented by computer-executable program instructions. Likewise, some blocks of the block diagrams and flow diagrams may not necessarily need to be performed in the order presented, may be repeated, or may not necessarily need to be performed at all, according to some examples or implementations of the disclosed technology.

While the present disclosure has been described in connection with a plurality of example aspects, as illustrated in the various figures and discussed above, it is understood that other similar aspects can be used, or modifications and additions can be made to the described aspects for performing the same function of the present disclosure without deviating therefrom. For example, in various aspects of the disclosure, methods and compositions were described according to aspects of the presently disclosed subject matter. However, other equivalent methods or composition to these described aspects are also contemplated by the teachings herein. Therefore, the present disclosure should not be limited to any single aspect, but rather construed in breadth and scope in accordance with the appended claims.

Example Use Cases

The following examples describe examples of a typical user flow pattern. They are intended solely for explanatory purposes and not limitation.

During the night time, an air conditioning system (i.e., cooling system 100) in a user's house can being on/off cycling at a lower cooling load due to the lower temperature outside. Due to lower energy load, as a system response the TXV lowers the flow rate of the refrigerant, lowering the pressure and temperature of the refrigerant 210 entering the evaporator. Upon detecting that the refrigerant has decreased in temperature (i.e., below the melting point of the phase-changing material 220), a valve (i.e., valve 230) can begin opening to allow a portion of the refrigerant to enter a heat exchanger (i.e., heat exchanger system 200). In the heat exchanger, the refrigerant can thermally communicate with a phase-changing material (i.e., phase-changing material 220) to induce a phase change of the phase-changing material from liquid to solid. Such a process can continue until the temperature of the refrigerant increases and the two materials reach thermal equilibrium. Upon detecting that the refrigerant and solidified phase-changing material are in thermal equilibrium, the valve can close to effectively store the cooling energy in the phase-changing material.

During the day time, the air conditioning system in a user's house can continue cooling and experience a high energy load due to the effects of the sun and higher external temperature. Such high-load operation can increase the flow rate of the refrigerant, and thereby the suction pressure and temperature of the refrigerant, as the air conditioning system operates to cool the user's house. Upon detecting that the refrigerant has increased in temperature (i.e., above the melting point of the phase-changing material 220), the valve can begin opening once more to allow a portion of the refrigerant to enter the heat exchanger. In the heat exchanger, the refrigerant can thermally communicate with the solidified phase-changing material to induce a phase change of the phase-changing material from solid to liquid. Such a process can also decrease the temperature of the refrigerant until the two materials reach thermal equilibrium. The decreased temperature of the refrigerant can increase the performance of the air conditioning system by adding additional cooling energy to the system without requiring extra energy to be exerted on the system. Upon detecting that the refrigerant and the liquefied phase-changing material are in thermal equilibrium, the valve can close to not expend more cooling power from the refrigerant to the phase-changing material.

By way of another example, a refrigerator can be operating with a working fluid of R-134a. While the door remains closed, the insulation of the refrigerator can retain the cold interior temperatures, reducing the need for additional cooling power. During this time, the cycling R-134a can remain cold as it is not being used in an evaporator to provide cooling power to the refrigerator. A valve can detect that the R-134a is cycling below the melting point of formic acid, which is 7.8° C. The valve can then allow a portion of the R-134a to enter a heat exchanger also containing the formic acid. While the cold R-134a is in thermal communication with the formic acid, the formic acid can solidify. The solidification process can give off a large amount of latent heat, thus increasing the temperature of the R-134a until the materials are in thermal equilibrium. Once thermal equilibrium is reached, the valve can close to effectively store cooling power in the solidified formic acid.

If a user opens the refrigerator door for a long period of time, a large amount of cooling power may be needed to retain the cool temperatures in the refrigerator. As the R-134a begins to be exerted by the evaporator to cool the refrigerator, the temperature of the R-134a can increase above the melting point of the formic acid. Upon detecting this increase, the valve can then allow a portion of the R-134a to enter the heat exchanger. While the warm R-134a is in thermal communication with the formic acid, the formic acid can liquefy. The liquefication process can absorb a large amount of latent heat, thus decreasing the temperature of the R-134a until the materials are in thermal equilibrium. The decreased temperature of the R-134a can therefore increase the performance of the refrigerator without requiring extra energy to be exerted on the system. Once thermal equilibrium is reached, the valve can close to prevent additional cooling power from being expended by the R-134a. 

What is claimed is:
 1. A heat exchanger system for use with a cooling system, the heat exchanger system comprising: a phase-changing material in thermal communication with a refrigerant flow path that is configured to permit refrigerant to flow therethrough; and a valve configured to selectively permit an amount of the refrigerant to flow through the refrigerant flow path, the amount of the refrigerant being based on a temperature difference between the refrigerant and the phase-changing material.
 2. The heat exchanger system of claim 1, further comprising a controller in communication with the valve and one or more sensors, the controller being configured to: receive temperature data from the one or more sensors; and control the valve based on the temperature data.
 3. The heat exchanger system of claim 1, wherein the phase-changing material has a melting point such that an absolute difference between the melting point of the phase-changing material and the median refrigerant temperature of the refrigerant is in the range from approximately 0° F. to approximately 10° F.
 4. The heat exchanger system of claim 1, wherein the valve has a degree of openness corresponding to the temperature difference between the refrigerant and the phase-changing material.
 5. The heat exchanger system of claim 4, wherein the valve has an open state and a closed state, and wherein the degree of openness is completely open in the open state and completely closed in the closed state.
 6. The heat exchanger system of claim 5, wherein the valve is configured to transition to the closed state when the median refrigerant temperature of the refrigerant and a temperature of the phase-changing material are substantially equivalent.
 7. The heat exchanger system of claim 6, wherein the valve is configured to transition to the open state when a difference between the temperature of the phase-changing material and the median refrigerant temperature of the refrigerant is greater than a predetermined threshold.
 8. The heat exchanger system of claim 7, wherein the degree of openness is proportional to the difference between the temperature of the phase-changing material and the median refrigerant temperature of the refrigerant.
 9. The heat exchanger system of claim 1, wherein the phase-changing material has a latent heat of fusion from 200 kJ/kg to 400 kJ/kg.
 10. A cooling system comprising: a refrigerant flow path; a refrigerant configured to flow through the refrigerant flow path; a compressor in fluid communication with the refrigerant flow path; a condenser in fluid communication with the refrigerant flow path; an evaporator in fluid communication with the refrigerant flow path; a thermal expansion valve in fluid communication with the refrigerant flow path; and a heat exchanger comprising: a phase-changing material in thermal communication with the refrigerant flow path, the phase-changing material being fluidly separated from the refrigerant; and a valve configured to selectively permit an amount of the refrigerant to flow through the heat exchanger system, the amount of the refrigerant corresponding to a temperature difference between the refrigerant and the phase-changing material.
 11. The cooling of claim 10, further comprising a controller in communication with the valve and one or more sensors, the controller being configured to: receive temperature data from the one or more sensors; and control the valve based on the temperature data.
 12. The cooling system of claim 10, wherein the phase-changing material has a melting point such that a difference between the melting point of the phase-changing material and the median refrigerant temperature is in the range from approximately 0° F. to approximately 10° F.
 13. The cooling system of claim 10, wherein the valve is configured to transition between a plurality of states.
 14. The cooling system of claim 13, wherein the plurality of states includes an open state, a closed state, and one or more intermediate states.
 15. The cooling system of claim 14, wherein the one or more intermediate states correspond to a difference between a temperature of the phase-changing material and a median refrigerant temperature of the refrigerant.
 16. The cooling system of claim 14, wherein the valve is configured to enter the closed state when a median refrigerant temperature of the refrigerant and a temperature of the phase-changing material are substantially equivalent.
 17. The cooling system of claim 15, wherein the valve is configured to transition to the open state when a difference between the temperature of the phase-changing material and the median refrigerant temperature of the refrigerant is greater than a predetermined threshold.
 18. A method of capturing cooling energy during partial-load cycles in a cooling system, the method comprising: responsive to a median refrigerant temperature of a refrigerant of the cooling system being less than a melting point of a phase-changing material, transitioning a valve to an open state such that the refrigerant can flow through a heat exchanger of the cooling system, thereby effecting heat transfer between the refrigerant and the phase-change material to cause the phase-changing material to become at least partially solidified; and responsive to the phase-changing material reaching thermal equilibrium with the median refrigerant temperature of the refrigerant, transitioning the valve to a closed state.
 19. The method of claim 18, further comprising: responsive to the median refrigerant temperature of the refrigerant being greater than the melting point of the phase-changing material, transitioning the valve to the open state such that the refrigerant can flow through the heat exchanger, thereby effecting heat transfer between the refrigerant and the phase-change material to cause the phase-changing material to become at least partially melted; and responsive to the phase-changing material reaching thermal equilibrium with the median refrigerant temperature of the refrigerant, transitioning the valve to the closed state.
 20. The method of claim 18, wherein the phase-changing material has a latent heat of fusion from 200 kJ/kg to 400 kJ/kg. 